1. Field of the Invention
The present invention relates to a tissue treatment device with a bandage that is essentially transparent to a predetermined range of wavelengths in the infrared (IR) range of the electromagnetic spectrum, and to a heater that emits energy primarily in the IR range. The bandage and heater are connected or joined by an attachment means that holds the heater in position on or over the bandage.
2. Description of the Related Art
Heat therapy has been used to treat tissue since the days of Hippocrates, with varying results. For example, heat therapy for wounds has involved the application of heat under conditions that make the tissues of a wound hyperthermic. However, hyperthermia impedes wound healing and may actually damage the wound tissues.
The xe2x80x9cnormalxe2x80x9d range of temperature for the human body is 37xc2x0 C.+1 C. (36xc2x0 C. to 38xc2x0 C.). This is termed the xe2x80x9cnormothermicxe2x80x9d range. Humans exhibit a thermoregulatory response to core temperature changes as little as xc2x11xc2x0 C., wherein xe2x80x9ccorexe2x80x9d as used herein refers to interior portions of the body. This extremely tight temperature control is necessary because virtually all human cellular functions, chemical reactions and enzymatic reactions are optimum at 37xc2x0 C. It should be understood that these are human temperature ranges and that different xe2x80x9cnormothermicxe2x80x9d ranges exist for different animal types, resulting in a different target temperature range.
Surface tissue varies in temperature according to where on the body it is located. For example, in humans, the skin of the torso is usually hypothermic, while the skin of the legs is always hypothermic. The normal skin temperature of the distal leg is approximately 32xc2x0 C., which is considered to be xe2x80x9cmoderately hypothermic.xe2x80x9d The skin temperature of the distal leg of a patient with vascular insufficiency may be as low as 25xc2x0 C., which is xe2x80x9cseverely hypothermicxe2x80x9d The hypothermic condition of wounds and ulcers inhibits healing. Severely hypothermic skin or wound tissue is in a state that may be termed xe2x80x9csuspended animation.xe2x80x9d In suspended animation, tissue is living, but cellular functions necessary for cell division and collagen deposition are slowed or even stopped. Further, the immune system is inhibited, allowing wounds to become heavily colonized with bacteria. The local application of heat to hypothermic tissue will cause some degree of vasodilatation, resulting in an increase in local blood flow. Increased blood flow increases the subcutaneous oxygen tension (PsqO2) which, in turn, increases both collagen deposition and immune function.
Many references report that the immune system is inhibited by hypothermia and activated by mild hyperthermia (fever). Persp Biol Med:439-474, Spring 1980, reports that local body temperature is a critical factor determining host susceptibility, the location of lesions and contracting infectious diseases. New Eng J Med 305:808-814, 1981, reports that animals exposed to cold environments are more susceptible to infectious diseases, whereas exposure to high ambient temperatures often produces a beneficial result. Wound Rep Reg 2:48-56, 1994 and Acta Anaesth Scand 38:201-205, 1994, report that infections caused by a standard inoculum of E. coli or S. aureus were significantly more severe in hypothermic guinea pigs than in normothermic control animals. New Eng J Med 334:1209-1215, 1996, reports that hypothermic colorectal surgical patients had three times more wound infections (19% vs. 6%) than those who were kept normothermic during surgery with a Bair Hugger(copyright) patient warming system described in commonly assigned U.S. Pat. Nos. 5,324,320, 5,300,102 and 5,350,417. Further, six weeks of warming therapy with the Bair Hugger(copyright) patient warming system has successfully healed chronic progressive ulcers which heretofore have been resistant to standard therapies.
Currently available medical devices that apply heat to wounds include infrared lights, warm water pads, warm water bottles, whirlpools and Sitz baths. All types of lesions, such as surgical, chronic, traumatic, donor sites, infected wounds and burns, have been treated with these warming modalities. Particularly difficult has been the application of heat to open wounds such as ulcers. Treatment of a wound with infrared light requires that the wound be positioned under the light during therapy, necessitating patient immobility. Further, the infrared heat treatment accelerates the drying of the wound, thereby slowing the healing process. Warm water pads and bottles and electrical heating pads are cumbersome, reduce patient mobility, and are usually applied to the extremities and held in place with inconvenient wraps such as straps, hook-and-eye material or tabs. Whirlpools and Sitz baths reduce mobility and limit the duration of warming therapy due to skin maceration by the water. None of these modalities, with the exception of electrical heating pads, is capable of prolonged heat treatment of a wound.
Each of the various kinds of body tissue, such as epidermal, muscle, and fatty tissue, has a different water content. Epidermal tissue contains a relatively large proportion of water and is known to absorb greater amounts of IR energy at wavelengths of less than 3 microns (xcexcm) due to the water content. Therefore, when an IR radiation apparatus is used to heat a wound area, it is primarily the skin region that is heated. Many chronic wounds, such as pressure wounds, result from bony prominence pressure points in patients who remain immobile for long periods of time. Other subdermal injuries result in occluded blood flow, either venous or arterial, which deprive the wound area of oxygen. Although such wounds may eventually erupt to the skin surface, the primary wound area is beneath the skin. Because IR radiation primarily affects the skin, IR wound treatment has largely been ineffective for subdermal wounds.
There is a need for an apparatus to treat tissue, especially subdermal tissue with heat for a prolonged period of time, while promoting patient convenience and mobility. For example, such treatment would be used to produce a substantially normothermic condition at a wound. Such an apparatus should selectively transfer heat to the epidermis, passing beneficial (therapeutic) radiation and blocking radiation that is harmful, be convenient to operate without interfering with the patient""s movement or comfort, and be capable of maintaining a moist tissue environment. Such an apparatus should be able to heat subdermal tissue areas without burning the overlying epidermal tissue.
Preferably, the placement of the apparatus is confined to a xe2x80x9ctissue treatment areaxe2x80x9d. Such an area may include, for example, a wound, or skin adjacent the wound (the periwound), or both. Such a treatment area may be any area of tissue to which heat is applied for any clinical purpose.
The invention is a tissue treatment apparatus that includes a bandage that is transparent or at least transmissive in a predetermined range of wavelengths in the infrared (IR) range of the electromagnetic spectrum. A heater is disposed on or over the bandage. The heater emits a significant amount of its energy in the IR range at a frequency that is dependent on the surface temperature of the heater. An attachment means holds the heater in position over the bandage.
Other objects and advantages of the invention will become apparent upon reading the following description taken together with the accompanying drawings.